a) Field of the Invention
The present invention relates to an articulated robot. Furthermore, the present invention relates to an articulated robot which transfers a workpiece, such as a semiconductor wafer.
b) Description of the Related Art
An articulated robot is used for transferring a workpiece such as a semiconductor wafer from a cassette to a processing device for photo lithography, deposition and etching. For example, as shown in FIG. 16(A), articulated robot 100 comprises base 101, first arm 102, which is rotatably supported by base 101, second arm 103, which is rotatably supported by first arm 102, and hand portion 104 which is supported by the end of second arm 103. Articulated robot 100 transfers workpiece 107 from cassette 105 to processing device 106.
In the case where a semiconductor wafer is used as workpiece 107, it is necessary to maintain the direction of workpiece 107 for a thermal processing and deposition since the crystals of each semiconductor wafer have a directional property. Therefore, it is required to keep all workpieces 107, . . . , 107 on processing device 106 in the same direction when they are transferred.
For the above reasons, a mark, such as a notch and a D flat, is formed at a given position on the edge of workpiece 107 while a workpiece rotating device, called aligner 108, having a means to detect the mark is formed, separate from cassette 105 and processing device 106 as shown in FIG. 16. As shown in FIGS. (A) through (C), workpiece 107, which is removed from cassette 105 by hand portion 104, is first mounted on aligner 108 (FIG.(D)); after the direction of the workpiece is aligned in a given direction by turning it, workpiece 107 is transferred to and mounted on processing device 106 in a given direction (FIGS. (E) and (F)).
However, as shown in FIG. 17, if base 101 is formed such that workpiece 107 can be transferred by sliding to each of processing devices 106, . . . , 106, which are connected in parallel, the time required to transfer workpiece 107 becomes longer. In other words, it is necessary for workpieces 107, . . . , 107 to pass through aligner 108 to align the workpieces in one direction, and there is usually only one aligner 108 for two cassettes 105, 105 and a plurality of processing devices 106, . . . , 106. Therefore, if one wants to transfer workpiece 107 from lower cassette 105 to processing device 106 at the bottom in the figure, workpiece 107 must pass through aligner 108; as a result, distance of transfer by robot 100 becomes longer such that it takes a longer time for workpiece 107 to be transferred.
Also, if one wants to transfer workpiece 107 from upper cassette 105 to processing device 106 at the top in the figure, workpiece 107 cannot be transferred until the orientation for alignment by aligner 108 is complete; therefore, robot 100 shall be idling while the orientation is carried out.
On the other hand, articulated robot 100, which transfers a workpiece such as a semiconductor wafer from a cassette to a processing device and vice versa, generally comprises two arms 102, 103 and hand portion 104, as shown in FIG. 18, such that workpiece 107 can be transferred along a linear path. In the case of such an articulated robot 100, or articulated robot 100 having three arms 102, 103, 113 as shown in FIG. 19, hand portion 104 holding workpiece 107 is linearly transferred in the axial direction of the hand portion such that workpiece 107 can be transferred without being rotated.
There are known transportation mechanisms such as a belt and pulley, in which two arms 102, 103 can be formed to be mechanically connected, as a means to linearly move hand portion 104. Due to these mechanisms, articulated robot 100 limits movements of arms 102, 103 (, 113). Additionally, each of workpieces 107 mounted at various positions in a connected plurality of cassettes can be transferred from each position by being held by hand portion 104.
However, when hand portion 104 is transferred while the axis of hand portion 104 passes through the vicinity of the rotational center of arm 102, that is, when the center of transferred workpiece 107 shows a path passing the vicinity of rotational center 116, a rapid rotation of arm 102 is required at rotational center 116 of arm 102, and such a position is called a singularity. As a result, an excessive load may be caused in the movement of arms 102, 103 of the above mechanism. In other words, as shown in FIGS. 20(A) through (C), when support point 117 of hand portion 104 passes the vicinity of rotational center (singularity) 116 of arm 102, each of arms 102, 103 are required to move around rotational center (singularity) 116 for about 180 degree. Additionally, if workpiece 107 is transferred at a constant speed, each of arms 102, 103 must be rapidly and vigorously rotated such that unnatural movement will be caused therein. This phenomena is also observed in articulated robot 100 having three arms 102, 103, 113 and hand portion 104 as shown in FIG. 21.
On the other hand, as shown in FIG. 22, articulated robot 100 having direct-acting mechanism 119 capable of a horizontal transfer together with base 121 has been suggested. According to this mechanism, horizontal transfer of workpiece 107 is possible while hand portion 104 is distant from rotational center 116 of arm 102. Consequently, hand portion 104 does not have to pass the vicinity of rotational center 116 of arm 102; thus, the above problems related to the generation of a singularity can be solved. Nonetheless, to form articulated robot 100 such that it is capable of a linear movement including base 121, a space for direct-acting mechanism 119 is needed. In addition to dust generated by direct-acting mechanism 119 during transfer, it is difficult to seal the dust inside the robot such that the robot is not able to be used in a clean room.
Therefore, a primary object of the present invention is to improve the above problems which an articulated robot to transfer a workpiece, such as a semiconductor wafer, conventionally has had. More specifically, the present invention intends to provide an articulated robot in which workpieces can be transferred while orientation of the workpieces is carried out such that efficiency of transfer of workpieces is improved. Another object is to provide an articulated robot in which transfer of workpieces can be carried out without unnatural movement in arms and generation of dust is minimized during transfer of workpieces.
In accordance with the invention, an articulated robot comprises a movable first transferring portion and a second transferring portion movably supported in relation to the movable first transferring portion by a joint portion. A workpiece is positioned at a position, where a workpiece positional deviation detecting means is located, by a hand portion formed at an end of the second transferring portion. The workpiece positional deviation detecting means detects the amount of deviation in the position of the workpiece. A positioning portion of the workpiece and a sensor portion for detecting deviations of the workpiece are formed either at the first transferring portion or the second transferring portion which form the articulated robot. A detecting operation by the sensor portion and transferring of the first and second transferring portions are enabled when the workpiece is positioned at the positioning portion of the articulated robot.